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Linux/net/core/datagram.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *      SUCS NET3:
  4  *
  5  *      Generic datagram handling routines. These are generic for all
  6  *      protocols. Possibly a generic IP version on top of these would
  7  *      make sense. Not tonight however 8-).
  8  *      This is used because UDP, RAW, PACKET, DDP, IPX, AX.25 and
  9  *      NetROM layer all have identical poll code and mostly
 10  *      identical recvmsg() code. So we share it here. The poll was
 11  *      shared before but buried in udp.c so I moved it.
 12  *
 13  *      Authors:        Alan Cox <alan@lxorguk.ukuu.org.uk>. (datagram_poll() from old
 14  *                                                   udp.c code)
 15  *
 16  *      Fixes:
 17  *              Alan Cox        :       NULL return from skb_peek_copy()
 18  *                                      understood
 19  *              Alan Cox        :       Rewrote skb_read_datagram to avoid the
 20  *                                      skb_peek_copy stuff.
 21  *              Alan Cox        :       Added support for SOCK_SEQPACKET.
 22  *                                      IPX can no longer use the SO_TYPE hack
 23  *                                      but AX.25 now works right, and SPX is
 24  *                                      feasible.
 25  *              Alan Cox        :       Fixed write poll of non IP protocol
 26  *                                      crash.
 27  *              Florian  La Roche:      Changed for my new skbuff handling.
 28  *              Darryl Miles    :       Fixed non-blocking SOCK_SEQPACKET.
 29  *              Linus Torvalds  :       BSD semantic fixes.
 30  *              Alan Cox        :       Datagram iovec handling
 31  *              Darryl Miles    :       Fixed non-blocking SOCK_STREAM.
 32  *              Alan Cox        :       POSIXisms
 33  *              Pete Wyckoff    :       Unconnected accept() fix.
 34  *
 35  */
 36 
 37 #include <linux/module.h>
 38 #include <linux/types.h>
 39 #include <linux/kernel.h>
 40 #include <linux/uaccess.h>
 41 #include <linux/mm.h>
 42 #include <linux/interrupt.h>
 43 #include <linux/errno.h>
 44 #include <linux/sched.h>
 45 #include <linux/inet.h>
 46 #include <linux/netdevice.h>
 47 #include <linux/rtnetlink.h>
 48 #include <linux/poll.h>
 49 #include <linux/highmem.h>
 50 #include <linux/spinlock.h>
 51 #include <linux/slab.h>
 52 #include <linux/pagemap.h>
 53 #include <linux/uio.h>
 54 
 55 #include <net/protocol.h>
 56 #include <linux/skbuff.h>
 57 
 58 #include <net/checksum.h>
 59 #include <net/sock.h>
 60 #include <net/tcp_states.h>
 61 #include <trace/events/skb.h>
 62 #include <net/busy_poll.h>
 63 
 64 #include "datagram.h"
 65 
 66 /*
 67  *      Is a socket 'connection oriented' ?
 68  */
 69 static inline int connection_based(struct sock *sk)
 70 {
 71         return sk->sk_type == SOCK_SEQPACKET || sk->sk_type == SOCK_STREAM;
 72 }
 73 
 74 static int receiver_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,
 75                                   void *key)
 76 {
 77         /*
 78          * Avoid a wakeup if event not interesting for us
 79          */
 80         if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
 81                 return 0;
 82         return autoremove_wake_function(wait, mode, sync, key);
 83 }
 84 /*
 85  * Wait for the last received packet to be different from skb
 86  */
 87 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 88                                 const struct sk_buff *skb)
 89 {
 90         int error;
 91         DEFINE_WAIT_FUNC(wait, receiver_wake_function);
 92 
 93         prepare_to_wait_exclusive(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
 94 
 95         /* Socket errors? */
 96         error = sock_error(sk);
 97         if (error)
 98                 goto out_err;
 99 
100         if (sk->sk_receive_queue.prev != skb)
101                 goto out;
102 
103         /* Socket shut down? */
104         if (sk->sk_shutdown & RCV_SHUTDOWN)
105                 goto out_noerr;
106 
107         /* Sequenced packets can come disconnected.
108          * If so we report the problem
109          */
110         error = -ENOTCONN;
111         if (connection_based(sk) &&
112             !(sk->sk_state == TCP_ESTABLISHED || sk->sk_state == TCP_LISTEN))
113                 goto out_err;
114 
115         /* handle signals */
116         if (signal_pending(current))
117                 goto interrupted;
118 
119         error = 0;
120         *timeo_p = schedule_timeout(*timeo_p);
121 out:
122         finish_wait(sk_sleep(sk), &wait);
123         return error;
124 interrupted:
125         error = sock_intr_errno(*timeo_p);
126 out_err:
127         *err = error;
128         goto out;
129 out_noerr:
130         *err = 0;
131         error = 1;
132         goto out;
133 }
134 EXPORT_SYMBOL(__skb_wait_for_more_packets);
135 
136 static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
137 {
138         struct sk_buff *nskb;
139 
140         if (skb->peeked)
141                 return skb;
142 
143         /* We have to unshare an skb before modifying it. */
144         if (!skb_shared(skb))
145                 goto done;
146 
147         nskb = skb_clone(skb, GFP_ATOMIC);
148         if (!nskb)
149                 return ERR_PTR(-ENOMEM);
150 
151         skb->prev->next = nskb;
152         skb->next->prev = nskb;
153         nskb->prev = skb->prev;
154         nskb->next = skb->next;
155 
156         consume_skb(skb);
157         skb = nskb;
158 
159 done:
160         skb->peeked = 1;
161 
162         return skb;
163 }
164 
165 struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
166                                           struct sk_buff_head *queue,
167                                           unsigned int flags,
168                                           void (*destructor)(struct sock *sk,
169                                                            struct sk_buff *skb),
170                                           int *off, int *err,
171                                           struct sk_buff **last)
172 {
173         bool peek_at_off = false;
174         struct sk_buff *skb;
175         int _off = 0;
176 
177         if (unlikely(flags & MSG_PEEK && *off >= 0)) {
178                 peek_at_off = true;
179                 _off = *off;
180         }
181 
182         *last = queue->prev;
183         skb_queue_walk(queue, skb) {
184                 if (flags & MSG_PEEK) {
185                         if (peek_at_off && _off >= skb->len &&
186                             (_off || skb->peeked)) {
187                                 _off -= skb->len;
188                                 continue;
189                         }
190                         if (!skb->len) {
191                                 skb = skb_set_peeked(skb);
192                                 if (IS_ERR(skb)) {
193                                         *err = PTR_ERR(skb);
194                                         return NULL;
195                                 }
196                         }
197                         refcount_inc(&skb->users);
198                 } else {
199                         __skb_unlink(skb, queue);
200                         if (destructor)
201                                 destructor(sk, skb);
202                 }
203                 *off = _off;
204                 return skb;
205         }
206         return NULL;
207 }
208 
209 /**
210  *      __skb_try_recv_datagram - Receive a datagram skbuff
211  *      @sk: socket
212  *      @flags: MSG\_ flags
213  *      @destructor: invoked under the receive lock on successful dequeue
214  *      @off: an offset in bytes to peek skb from. Returns an offset
215  *            within an skb where data actually starts
216  *      @err: error code returned
217  *      @last: set to last peeked message to inform the wait function
218  *             what to look for when peeking
219  *
220  *      Get a datagram skbuff, understands the peeking, nonblocking wakeups
221  *      and possible races. This replaces identical code in packet, raw and
222  *      udp, as well as the IPX AX.25 and Appletalk. It also finally fixes
223  *      the long standing peek and read race for datagram sockets. If you
224  *      alter this routine remember it must be re-entrant.
225  *
226  *      This function will lock the socket if a skb is returned, so
227  *      the caller needs to unlock the socket in that case (usually by
228  *      calling skb_free_datagram). Returns NULL with @err set to
229  *      -EAGAIN if no data was available or to some other value if an
230  *      error was detected.
231  *
232  *      * It does not lock socket since today. This function is
233  *      * free of race conditions. This measure should/can improve
234  *      * significantly datagram socket latencies at high loads,
235  *      * when data copying to user space takes lots of time.
236  *      * (BTW I've just killed the last cli() in IP/IPv6/core/netlink/packet
237  *      *  8) Great win.)
238  *      *                                           --ANK (980729)
239  *
240  *      The order of the tests when we find no data waiting are specified
241  *      quite explicitly by POSIX 1003.1g, don't change them without having
242  *      the standard around please.
243  */
244 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
245                                         void (*destructor)(struct sock *sk,
246                                                            struct sk_buff *skb),
247                                         int *off, int *err,
248                                         struct sk_buff **last)
249 {
250         struct sk_buff_head *queue = &sk->sk_receive_queue;
251         struct sk_buff *skb;
252         unsigned long cpu_flags;
253         /*
254          * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
255          */
256         int error = sock_error(sk);
257 
258         if (error)
259                 goto no_packet;
260 
261         do {
262                 /* Again only user level code calls this function, so nothing
263                  * interrupt level will suddenly eat the receive_queue.
264                  *
265                  * Look at current nfs client by the way...
266                  * However, this function was correct in any case. 8)
267                  */
268                 spin_lock_irqsave(&queue->lock, cpu_flags);
269                 skb = __skb_try_recv_from_queue(sk, queue, flags, destructor,
270                                                 off, &error, last);
271                 spin_unlock_irqrestore(&queue->lock, cpu_flags);
272                 if (error)
273                         goto no_packet;
274                 if (skb)
275                         return skb;
276 
277                 if (!sk_can_busy_loop(sk))
278                         break;
279 
280                 sk_busy_loop(sk, flags & MSG_DONTWAIT);
281         } while (sk->sk_receive_queue.prev != *last);
282 
283         error = -EAGAIN;
284 
285 no_packet:
286         *err = error;
287         return NULL;
288 }
289 EXPORT_SYMBOL(__skb_try_recv_datagram);
290 
291 struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
292                                     void (*destructor)(struct sock *sk,
293                                                        struct sk_buff *skb),
294                                     int *off, int *err)
295 {
296         struct sk_buff *skb, *last;
297         long timeo;
298 
299         timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
300 
301         do {
302                 skb = __skb_try_recv_datagram(sk, flags, destructor, off, err,
303                                               &last);
304                 if (skb)
305                         return skb;
306 
307                 if (*err != -EAGAIN)
308                         break;
309         } while (timeo &&
310                 !__skb_wait_for_more_packets(sk, err, &timeo, last));
311 
312         return NULL;
313 }
314 EXPORT_SYMBOL(__skb_recv_datagram);
315 
316 struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned int flags,
317                                   int noblock, int *err)
318 {
319         int off = 0;
320 
321         return __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
322                                    NULL, &off, err);
323 }
324 EXPORT_SYMBOL(skb_recv_datagram);
325 
326 void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
327 {
328         consume_skb(skb);
329         sk_mem_reclaim_partial(sk);
330 }
331 EXPORT_SYMBOL(skb_free_datagram);
332 
333 void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
334 {
335         bool slow;
336 
337         if (!skb_unref(skb)) {
338                 sk_peek_offset_bwd(sk, len);
339                 return;
340         }
341 
342         slow = lock_sock_fast(sk);
343         sk_peek_offset_bwd(sk, len);
344         skb_orphan(skb);
345         sk_mem_reclaim_partial(sk);
346         unlock_sock_fast(sk, slow);
347 
348         /* skb is now orphaned, can be freed outside of locked section */
349         __kfree_skb(skb);
350 }
351 EXPORT_SYMBOL(__skb_free_datagram_locked);
352 
353 int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
354                         struct sk_buff *skb, unsigned int flags,
355                         void (*destructor)(struct sock *sk,
356                                            struct sk_buff *skb))
357 {
358         int err = 0;
359 
360         if (flags & MSG_PEEK) {
361                 err = -ENOENT;
362                 spin_lock_bh(&sk_queue->lock);
363                 if (skb->next) {
364                         __skb_unlink(skb, sk_queue);
365                         refcount_dec(&skb->users);
366                         if (destructor)
367                                 destructor(sk, skb);
368                         err = 0;
369                 }
370                 spin_unlock_bh(&sk_queue->lock);
371         }
372 
373         atomic_inc(&sk->sk_drops);
374         return err;
375 }
376 EXPORT_SYMBOL(__sk_queue_drop_skb);
377 
378 /**
379  *      skb_kill_datagram - Free a datagram skbuff forcibly
380  *      @sk: socket
381  *      @skb: datagram skbuff
382  *      @flags: MSG\_ flags
383  *
384  *      This function frees a datagram skbuff that was received by
385  *      skb_recv_datagram.  The flags argument must match the one
386  *      used for skb_recv_datagram.
387  *
388  *      If the MSG_PEEK flag is set, and the packet is still on the
389  *      receive queue of the socket, it will be taken off the queue
390  *      before it is freed.
391  *
392  *      This function currently only disables BH when acquiring the
393  *      sk_receive_queue lock.  Therefore it must not be used in a
394  *      context where that lock is acquired in an IRQ context.
395  *
396  *      It returns 0 if the packet was removed by us.
397  */
398 
399 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
400 {
401         int err = __sk_queue_drop_skb(sk, &sk->sk_receive_queue, skb, flags,
402                                       NULL);
403 
404         kfree_skb(skb);
405         sk_mem_reclaim_partial(sk);
406         return err;
407 }
408 EXPORT_SYMBOL(skb_kill_datagram);
409 
410 static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
411                                struct iov_iter *to, int len, bool fault_short,
412                                size_t (*cb)(const void *, size_t, void *,
413                                             struct iov_iter *), void *data)
414 {
415         int start = skb_headlen(skb);
416         int i, copy = start - offset, start_off = offset, n;
417         struct sk_buff *frag_iter;
418 
419         /* Copy header. */
420         if (copy > 0) {
421                 if (copy > len)
422                         copy = len;
423                 n = cb(skb->data + offset, copy, data, to);
424                 offset += n;
425                 if (n != copy)
426                         goto short_copy;
427                 if ((len -= copy) == 0)
428                         return 0;
429         }
430 
431         /* Copy paged appendix. Hmm... why does this look so complicated? */
432         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
433                 int end;
434                 const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
435 
436                 WARN_ON(start > offset + len);
437 
438                 end = start + skb_frag_size(frag);
439                 if ((copy = end - offset) > 0) {
440                         struct page *page = skb_frag_page(frag);
441                         u8 *vaddr = kmap(page);
442 
443                         if (copy > len)
444                                 copy = len;
445                         n = cb(vaddr + frag->page_offset +
446                                 offset - start, copy, data, to);
447                         kunmap(page);
448                         offset += n;
449                         if (n != copy)
450                                 goto short_copy;
451                         if (!(len -= copy))
452                                 return 0;
453                 }
454                 start = end;
455         }
456 
457         skb_walk_frags(skb, frag_iter) {
458                 int end;
459 
460                 WARN_ON(start > offset + len);
461 
462                 end = start + frag_iter->len;
463                 if ((copy = end - offset) > 0) {
464                         if (copy > len)
465                                 copy = len;
466                         if (__skb_datagram_iter(frag_iter, offset - start,
467                                                 to, copy, fault_short, cb, data))
468                                 goto fault;
469                         if ((len -= copy) == 0)
470                                 return 0;
471                         offset += copy;
472                 }
473                 start = end;
474         }
475         if (!len)
476                 return 0;
477 
478         /* This is not really a user copy fault, but rather someone
479          * gave us a bogus length on the skb.  We should probably
480          * print a warning here as it may indicate a kernel bug.
481          */
482 
483 fault:
484         iov_iter_revert(to, offset - start_off);
485         return -EFAULT;
486 
487 short_copy:
488         if (fault_short || iov_iter_count(to))
489                 goto fault;
490 
491         return 0;
492 }
493 
494 /**
495  *      skb_copy_and_hash_datagram_iter - Copy datagram to an iovec iterator
496  *          and update a hash.
497  *      @skb: buffer to copy
498  *      @offset: offset in the buffer to start copying from
499  *      @to: iovec iterator to copy to
500  *      @len: amount of data to copy from buffer to iovec
501  *      @hash: hash request to update
502  */
503 int skb_copy_and_hash_datagram_iter(const struct sk_buff *skb, int offset,
504                            struct iov_iter *to, int len,
505                            struct ahash_request *hash)
506 {
507         return __skb_datagram_iter(skb, offset, to, len, true,
508                         hash_and_copy_to_iter, hash);
509 }
510 EXPORT_SYMBOL(skb_copy_and_hash_datagram_iter);
511 
512 static size_t simple_copy_to_iter(const void *addr, size_t bytes,
513                 void *data __always_unused, struct iov_iter *i)
514 {
515         return copy_to_iter(addr, bytes, i);
516 }
517 
518 /**
519  *      skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
520  *      @skb: buffer to copy
521  *      @offset: offset in the buffer to start copying from
522  *      @to: iovec iterator to copy to
523  *      @len: amount of data to copy from buffer to iovec
524  */
525 int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
526                            struct iov_iter *to, int len)
527 {
528         trace_skb_copy_datagram_iovec(skb, len);
529         return __skb_datagram_iter(skb, offset, to, len, false,
530                         simple_copy_to_iter, NULL);
531 }
532 EXPORT_SYMBOL(skb_copy_datagram_iter);
533 
534 /**
535  *      skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
536  *      @skb: buffer to copy
537  *      @offset: offset in the buffer to start copying to
538  *      @from: the copy source
539  *      @len: amount of data to copy to buffer from iovec
540  *
541  *      Returns 0 or -EFAULT.
542  */
543 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
544                                  struct iov_iter *from,
545                                  int len)
546 {
547         int start = skb_headlen(skb);
548         int i, copy = start - offset;
549         struct sk_buff *frag_iter;
550 
551         /* Copy header. */
552         if (copy > 0) {
553                 if (copy > len)
554                         copy = len;
555                 if (copy_from_iter(skb->data + offset, copy, from) != copy)
556                         goto fault;
557                 if ((len -= copy) == 0)
558                         return 0;
559                 offset += copy;
560         }
561 
562         /* Copy paged appendix. Hmm... why does this look so complicated? */
563         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
564                 int end;
565                 const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
566 
567                 WARN_ON(start > offset + len);
568 
569                 end = start + skb_frag_size(frag);
570                 if ((copy = end - offset) > 0) {
571                         size_t copied;
572 
573                         if (copy > len)
574                                 copy = len;
575                         copied = copy_page_from_iter(skb_frag_page(frag),
576                                           frag->page_offset + offset - start,
577                                           copy, from);
578                         if (copied != copy)
579                                 goto fault;
580 
581                         if (!(len -= copy))
582                                 return 0;
583                         offset += copy;
584                 }
585                 start = end;
586         }
587 
588         skb_walk_frags(skb, frag_iter) {
589                 int end;
590 
591                 WARN_ON(start > offset + len);
592 
593                 end = start + frag_iter->len;
594                 if ((copy = end - offset) > 0) {
595                         if (copy > len)
596                                 copy = len;
597                         if (skb_copy_datagram_from_iter(frag_iter,
598                                                         offset - start,
599                                                         from, copy))
600                                 goto fault;
601                         if ((len -= copy) == 0)
602                                 return 0;
603                         offset += copy;
604                 }
605                 start = end;
606         }
607         if (!len)
608                 return 0;
609 
610 fault:
611         return -EFAULT;
612 }
613 EXPORT_SYMBOL(skb_copy_datagram_from_iter);
614 
615 int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
616                             struct iov_iter *from, size_t length)
617 {
618         int frag = skb_shinfo(skb)->nr_frags;
619 
620         while (length && iov_iter_count(from)) {
621                 struct page *pages[MAX_SKB_FRAGS];
622                 size_t start;
623                 ssize_t copied;
624                 unsigned long truesize;
625                 int n = 0;
626 
627                 if (frag == MAX_SKB_FRAGS)
628                         return -EMSGSIZE;
629 
630                 copied = iov_iter_get_pages(from, pages, length,
631                                             MAX_SKB_FRAGS - frag, &start);
632                 if (copied < 0)
633                         return -EFAULT;
634 
635                 iov_iter_advance(from, copied);
636                 length -= copied;
637 
638                 truesize = PAGE_ALIGN(copied + start);
639                 skb->data_len += copied;
640                 skb->len += copied;
641                 skb->truesize += truesize;
642                 if (sk && sk->sk_type == SOCK_STREAM) {
643                         sk->sk_wmem_queued += truesize;
644                         sk_mem_charge(sk, truesize);
645                 } else {
646                         refcount_add(truesize, &skb->sk->sk_wmem_alloc);
647                 }
648                 while (copied) {
649                         int size = min_t(int, copied, PAGE_SIZE - start);
650                         skb_fill_page_desc(skb, frag++, pages[n], start, size);
651                         start = 0;
652                         copied -= size;
653                         n++;
654                 }
655         }
656         return 0;
657 }
658 EXPORT_SYMBOL(__zerocopy_sg_from_iter);
659 
660 /**
661  *      zerocopy_sg_from_iter - Build a zerocopy datagram from an iov_iter
662  *      @skb: buffer to copy
663  *      @from: the source to copy from
664  *
665  *      The function will first copy up to headlen, and then pin the userspace
666  *      pages and build frags through them.
667  *
668  *      Returns 0, -EFAULT or -EMSGSIZE.
669  */
670 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
671 {
672         int copy = min_t(int, skb_headlen(skb), iov_iter_count(from));
673 
674         /* copy up to skb headlen */
675         if (skb_copy_datagram_from_iter(skb, 0, from, copy))
676                 return -EFAULT;
677 
678         return __zerocopy_sg_from_iter(NULL, skb, from, ~0U);
679 }
680 EXPORT_SYMBOL(zerocopy_sg_from_iter);
681 
682 /**
683  *      skb_copy_and_csum_datagram_iter - Copy datagram to an iovec iterator
684  *          and update a checksum.
685  *      @skb: buffer to copy
686  *      @offset: offset in the buffer to start copying from
687  *      @to: iovec iterator to copy to
688  *      @len: amount of data to copy from buffer to iovec
689  *      @csump: checksum pointer
690  */
691 static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
692                                       struct iov_iter *to, int len,
693                                       __wsum *csump)
694 {
695         return __skb_datagram_iter(skb, offset, to, len, true,
696                         csum_and_copy_to_iter, csump);
697 }
698 
699 /**
700  *      skb_copy_and_csum_datagram_msg - Copy and checksum skb to user iovec.
701  *      @skb: skbuff
702  *      @hlen: hardware length
703  *      @msg: destination
704  *
705  *      Caller _must_ check that skb will fit to this iovec.
706  *
707  *      Returns: 0       - success.
708  *               -EINVAL - checksum failure.
709  *               -EFAULT - fault during copy.
710  */
711 int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
712                                    int hlen, struct msghdr *msg)
713 {
714         __wsum csum;
715         int chunk = skb->len - hlen;
716 
717         if (!chunk)
718                 return 0;
719 
720         if (msg_data_left(msg) < chunk) {
721                 if (__skb_checksum_complete(skb))
722                         return -EINVAL;
723                 if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
724                         goto fault;
725         } else {
726                 csum = csum_partial(skb->data, hlen, skb->csum);
727                 if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
728                                                chunk, &csum))
729                         goto fault;
730 
731                 if (csum_fold(csum)) {
732                         iov_iter_revert(&msg->msg_iter, chunk);
733                         return -EINVAL;
734                 }
735 
736                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
737                     !skb->csum_complete_sw)
738                         netdev_rx_csum_fault(NULL, skb);
739         }
740         return 0;
741 fault:
742         return -EFAULT;
743 }
744 EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
745 
746 /**
747  *      datagram_poll - generic datagram poll
748  *      @file: file struct
749  *      @sock: socket
750  *      @wait: poll table
751  *
752  *      Datagram poll: Again totally generic. This also handles
753  *      sequenced packet sockets providing the socket receive queue
754  *      is only ever holding data ready to receive.
755  *
756  *      Note: when you *don't* use this routine for this protocol,
757  *      and you use a different write policy from sock_writeable()
758  *      then please supply your own write_space callback.
759  */
760 __poll_t datagram_poll(struct file *file, struct socket *sock,
761                            poll_table *wait)
762 {
763         struct sock *sk = sock->sk;
764         __poll_t mask;
765 
766         sock_poll_wait(file, sock, wait);
767         mask = 0;
768 
769         /* exceptional events? */
770         if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue))
771                 mask |= EPOLLERR |
772                         (sock_flag(sk, SOCK_SELECT_ERR_QUEUE) ? EPOLLPRI : 0);
773 
774         if (sk->sk_shutdown & RCV_SHUTDOWN)
775                 mask |= EPOLLRDHUP | EPOLLIN | EPOLLRDNORM;
776         if (sk->sk_shutdown == SHUTDOWN_MASK)
777                 mask |= EPOLLHUP;
778 
779         /* readable? */
780         if (!skb_queue_empty(&sk->sk_receive_queue))
781                 mask |= EPOLLIN | EPOLLRDNORM;
782 
783         /* Connection-based need to check for termination and startup */
784         if (connection_based(sk)) {
785                 if (sk->sk_state == TCP_CLOSE)
786                         mask |= EPOLLHUP;
787                 /* connection hasn't started yet? */
788                 if (sk->sk_state == TCP_SYN_SENT)
789                         return mask;
790         }
791 
792         /* writable? */
793         if (sock_writeable(sk))
794                 mask |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;
795         else
796                 sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
797 
798         return mask;
799 }
800 EXPORT_SYMBOL(datagram_poll);
801 

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